Stepped electrode assembly including stepped unit cell

ABSTRACT

There is provided a stepped electrode assembly including: a first electrode stack including at least one first unit cell, the first unit cell including at least one positive electrode and at least one negative electrode having the same area and being alternately stacked in a vertical direction with a separator disposed therebetween; and a second unit cell including at least one positive electrode and at least one negative electrode that are alternately stacked in the vertical direction with a separator disposed therebetween, the second unit cell disposed on a side of the first electrode stack with a separator disposed therebetween, wherein the second unit cell includes a first area electrode having the same area as an electrode area of the first electrode stack and a second area electrode having an area different from the area of the first area electrode, wherein the second unit cell is a stepped unit cell including a stepped portion formed by an area difference between the first and second area electrodes.

TECHNICAL FIELD

The present disclosure relates to an electrode assembly having a steppedportion, and more particularly, to an electrode assembly having anincreased degree of structural freedom in a thickness direction thereof.

BACKGROUND ART

In the related art, an electrode assembly is assembled by stacking aplurality of C-type or A-type bi-cells, each of the C-type or A-typebi-cells including electrodes having the same polarity and an electrodehaving a different polarity and disposed between the electrodes of thesame polarity.

Referring to FIG. 1, an electrode assembly 1 having stepped portions maybe assembled as follows: a first electrode stack is formed by stacking aplurality of bi-cells having the same area such as an A-type bi-cell 13and a C-type bi-cell 11 shown in FIG. 2; and a second electrode stack inwhich bi-cells having equal areas smaller than the area of eachelectrode of the first electrode stack is disposed on the firstelectrode stack. In this manner, a stepped electrode assembly having anarea decreasing in a vertical direction, such as the electrode assembly1 shown in FIG. 1, may be assembled.

DISCLOSURE Technical Problem

New types of devices having various designs require batteries having newdesigns. Therefore, there is increasing demand for batteries havingvarious designs.

Therefore, an aspect of the present disclosure may provide an electrodeassembly having an improved degree of structural freedom in thethickness direction thereof as compared with electrode assembliesassembled using bi-cells of the related art.

Technical Solution

According to an aspect of the present disclosure, a stepped electrodeassembly has an improved degree of structural freedom in the thicknessdirection thereof. The stepped electrode assembly may include: a firstelectrode stack including at least one first unit cell, the first unitcell including at least one positive electrode and at least one negativeelectrode having the same area and being alternately stacked in avertical direction with a separator disposed therebetween; and a secondunit cell including at least one positive electrode and at least onenegative electrode that are alternately stacked in the verticaldirection with a separator disposed therebetween, the second unit celldisposed on a side of the first electrode stack with a separatordisposed therebetween, wherein the second unit cell include a first areaelectrode having the same area as an electrode area of the firstelectrode stack and a second area electrode having an area differentfrom the area of the first area electrode, wherein the second unit cellis a stepped unit cell including a stepped portion formed by an areadifference between the first and second area electrodes.

The first and second area electrodes of the stepped unit cell may faceeach other, and one of the first and second area electrodes having acomparatively large area may be a negative electrode.

The stepped unit cell may be an A-type bi-cell including positiveelectrodes on both sides thereof and a negative electrode disposedtherebetween, or a C-type bi-cell including negative electrodes on bothsides thereof and a positive electrode disposed therebetween. Inaddition, the stepped unit cell may be a stacked type unit cell or astacked and folded type unit cell.

A second electrode stack including electrodes having the same area asthe area of the second area electrode of the stepped unit cell may bedisposed on the second area electrode of the stepped unit cell with aseparator disposed therebetween, and the second area electrode and anelectrode of the second electrode stack facing the second area electrodemay have different polarities.

A second electrode stack including electrodes having equal areasdifferent from the area of the second area electrode of the stepped unitcell may be disposed on the second area electrode of the stepped unitcell with separator disposed therebetween, and the second area electrodeand an electrode of the second electrode stack facing the second areaelectrode may have different polarities. In this case, a larger of thesecond area electrode and the electrode of the second electrode stackfacing the second area electrode may be a negative electrode.

A second stepped unit cell may be disposed on the second area electrodeof the stepped unit cell with a separator disposed therebetween, and anelectrode of the second stepped unit cell facing the second areaelectrode of the stepped unit cell may have the same area as the secondarea electrode but a polarity different from that of the second areaelectrode. In this case, a comparatively large electrode of the secondstepped unit cell may be a negative electrode.

A second stepped unit cell may be disposed on the second area electrodeof the stepped unit cell with a separator disposed therebetween, and anelectrode of the second stepped unit cell facing the second areaelectrode of the stepped unit cell may have an area and polaritydifferent from those of the second area electrode. In this case, alarger of the second area electrode and the electrode of the second unitcell facing the second area electrode may be a negative electrode, and acomparatively large electrode of the second stepped unit cell may be anegative electrode.

The electrode assembly may be a stacked type electrode assembly or astacked and folded type electrode assembly. In addition, each ofoutermost electrodes disposed on both sides of the electrode assemblymay be independently a negative electrode or a positive electrode. Inthis case, at least one of the outermost electrodes may be aone-side-coated electrode.

According to another aspect of the present disclosure, a secondarybattery may include the electrode assembly. The electrode assembly maybe disposed in a battery case. In this case, the battery case may be apouch type case. In addition, the secondary battery may be a lithium ionsecondary battery or a lithium ion polymer secondary battery.

According to another aspect of the present disclosure, a battery packmay include at least two secondary batteries such as the above-describedsecondary battery.

According to another aspect of the present disclosure, a device mayinclude one or more secondary batteries such as the above-describedsecondary battery. The device may be a cellular phone, a portablecomputer, a smartphone, a smartpad, a net book, an LEV (light electronicvehicle), an electric vehicle, a hybrid electric vehicle, a plug-inhybrid electric vehicle, or a power storage device.

Advantageous Effects

According to the present disclosure, since the stepped electrodeassembly is assembled using stepped bi-cells having stepped portions,the degree of structural freedom of the electrode assembly may beimproved in the thickness direction thereof.

Particularly, the degree of structural freedom of the electrode assemblymay be markedly improved because it is not required to use an evennumber of bi-cells for disposing negative electrodes as a comparativelylarge electrode and outermost electrodes when assembling the electrodeassembly.

In addition, since the degree of structural freedom of the electrodeassembly can be improved by using fewer mono-cells or without usingmono-cells, process errors caused by mono-cells bent when the mono-cellsare gripped in a feeding process of unit cells may be prevented.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating an electrode assembly havingstepped portions.

FIGS. 2A and 2B are schematic perspective views illustrating generalbi-cells used to form an electrode assembly, FIG. 2A illustrating anA-type bi-cell, FIG. 2B illustrating a C-type bi-cell.

FIG. 3 a schematic cross-sectional view illustrating an electrodeassembly assembled using bi-cells such as shown in FIGS. 2A and 2B.

FIG. 4 is a schematic perspective view illustrating a mono-cell used toform an electrode assembly.

FIG. 5 is a schematic cross-sectional view illustrating a comparativeexample of an electrode assembly having an improved degree of structuralfreedom in the thickness direction thereof, the electrode assembly beingassembled using bi-cells and mono-cells such as shown in FIGS. 2A and 2Band FIG. 4.

FIGS. 6A and 6B are schematic perspective views illustrating steppedbi-cells used to form an electrode assembly according to the presentdisclosure, FIG. 6A illustrating an A-type bi-cell, FIG. 6B illustratinga C-type bi-cell.

FIGS. 7A and 7B are schematic cross-sectional views illustrating steppedbi-cells used to form an electrode assembly according to the presentdisclosure, FIG. 7A illustrating an A-type bi-cell, FIG. 7B illustratinga C-type bi-cell.

FIG. 8 is a schematic cross-sectional view illustrating an electrodeassembly assembled using stepped bi-cells according to the presentdisclosure.

FIGS. 9A and 9B are schematic views illustrating bending of bi-cells andmono-cells when the bi-cells and the mono-cells are gripped in a feedingprocess, FIG. 9A illustrating bending of the bi-cells, FIG. 9Billustrating bending of the mono-cells.

BEST MODE

Generally, an electrode assembly having a stepped portion is assembledby stacking a plurality of C-type or A-type bi-cells, each of the C-typeor A-type Bi-cell including electrodes of the same polarity and anelectrode having a different polarity and disposed between theelectrodes of the same polarity.

For example, an electrode assembly 1 having stepped portions may beformed by assembling a first electrode stack 41 having a large size, asecond electrode stack 43 having a medium size, and a third electrodestack 45 having a small size in such a manner that the first and secondelectrode stacks 41 and 43 face each other and the second and thirdelectrode stacks 43 and 45 face each other as shown in FIG. 3. Atinterfaces of the first, second, and third electrode stacks 41, 43, and45 at which stepped portions are formed, the larger electrode stacks 41and 43 include negative electrodes 5 as interfacial electrodes, and thesmaller electrode stacks 43 and 45 include positive electrodes 3 asinterfacial electrodes. Therefore, electrodes having differentpolarities face each other at the interfaces of the first, second, andthird electrode stacks 41, 43, and 45.

In this case, as shown In FIG. 3, each of two or more electrode stacks(the second and third electrode stacks 43 and 45) to be disposed on thelowermost first electrode stack 41 may have an even number of bi-cells11 and 13 (2×n where n is an integer equal to or greater than 1).Therefore, there is a limitation when two or more electrode stacks (43and 45) to be disposed on the lowermost first electrode stack 41 cannotbe constituted by even numbers of bi-cells 11 and 13 due to the shape ofa device in which the electrode assembly 1 will be used.

The inventors have repeatedly conducted research to develop electrodeassemblies having an improved degree of design freedom in the thicknessdirection thereof. As a result; the inventors found that if an electrodeassembly is formed by assembling bi-cells having stepped portions, thethickness of the electrode assembly can be easily adjusted in a verticaldirection. That is, the degree of structural freedom of the electrodeassembly can be improved in the thickness direction thereof according torequirements of a device in which the electrode assembly will be used.The inventors have invented the present invention based on thisknowledge.

The present disclosure provides an electrode assembly including at leastone unit cell in which at least one positive electrode and at leastnegative electrode are vertically stacked with a separator disposedtherebetween. For example, as shown in FIG. 1, the present disclosureprovides an electrode assembly having stopped portions and improved inthe degree of freedom in the thickness direction thereof.

In the present disclosure, the electrode assembly having a steppedportion may be formed by stacking unit cells. That is, the electrodeassembly may be formed by stacking unit cells each including at leastone negative electrode, at least one positive electrode, and a separatordisposed between the negative and positive electrodes.

In the present disclosure, the unit cells are not limited to aparticular type. As shown in FIGS. 2A and 2B, examples of the unit cellsmay include: an A-type bi-cell 13 including positive electrodes 3 onboth sides thereof and a negative electrode 5 disposed therebetween; anda C-type bi-cell 11 including negative electrodes 5 on both sidesthereof and positive electrodes 3 disposed therebetween. In addition, asshown in FIG. 4, examples of the unit cells may include a mono-cell 15including a negative electrode 5, a positive electrode 3, and aseparator 7 disposed therebetween.

Bi-cells may be used as unit cells to reduce errors in a unit cellstacking process. That is, bi-cells each including three electrodes andtwo separators have a higher degree of stiffness than mono-cells eachincluding a negative electrode, a positive electrode, with a separatordisposed therebetween. As shown in FIGS. 9A and 9B, if mono-cells areused as unit cells to form an electrode assembly, the unit cells may bebent to cause process errors in a feeding process in which the unitcells are gripped and fed for stacking or arrangement. That is, ifbi-cells having a high degree of stiffness are used as unit cellsinstead of mono-cells, process errors may be decreased.

In the present disclosure, the electrode assembly is formed using theabove-described unit cells. In the electrode assembly, positive andnegative electrodes are alternately stacked in a vertical direction withseparators disposed therebetween, and one or more stepped portions areformed on the electrode assembly. Such a stepped portion may be formedon two layers of at least two kinds electrodes having different areas.For example, one or two stepped portions may be formed on two or threelayers by disposing a stepped unit cell on a first electrode stack,wherein the stepped unit cell includes at least one first area electrodehaving a first area and at least one second area electrode disposed onthe first area electrode and having a second area different from thefirst area.

In the present disclosure, the stepped unit cell may be a steppedbi-cell, and examples of the stepped bi-cell are shown in FIGS. 6A to7B. FIGS. 6A and 6B are perspective views illustrating stepped bi-cells21 and 23, and FIGS. 7A and 7B are cross-sectional views illustratingthe stepped bi-cells 21 and 23. The stepped bi-cell 23 illustrated inFIGS. 7A and 7B is an A-type stepped bi-cell including positiveelectrodes 3 on both sides thereof and a negative electrode 5 disposedtherebetween, and the stepped bi-cell 21 illustrated in FIGS. 6B and 7Bis a C-type stepped bi-cell including negative electrodes 5 on bothsides thereof and a positive electrode 3 disposed therebetween.

In each of the stepped bi-cells 21 and 23 shown in FIGS. 6A to 7B, astepped portion is formed by disposing a comparatively small positiveelectrode 3 on a comparatively large negative electrode 5. That is, thelarger of two interfacial electrodes at which a stepped portion isformed may be a negative electrode. As described above, if a negativeelectrode is the larger of two interfacial electrodes, lithium may notprecipitate from a positive electrode active material during chargingand discharging operations of a battery, and thus the stability of thebattery may not be deteriorated by the precipitation of lithium.

In the present disclosure, the stepped unit cell may be a steppedbi-cell as described above. Alternatively, the stepped unit cell may bea stepped mono-cell. However, as described above, a stepped bi-cell maybe favored as the stepped unit cell if errors in a feeding process areconsidered.

Conventional mono-cells not having stepped portions such as themono-cell 15 shown in FIG. 4 may be used to form an electrode assembly 1shown in FIG. 5. The electrode assembly 1 shown in FIG. 5 may have animproved degree of structural freedom as compared with the electrodeassembly 1 of FIG. 3 assembled by using the A-type and C-type bi-cells13 and 11. However, according to an embodiment of the presentdisclosure, stepped bi-cells 31 and 33 such as the stepped bi-cells 21and 23 shown in FIGS. 6A to 7B may be used to form an electrode assembly1 shown in FIG. 8. Referring to FIGS. 5 and 8, the electrode assembly 1formed of the stepped bi-cells 31 and 33 according to the embodiment ofthe present disclosure has a small number of electrodes stacked in thethickness direction thereof as compared of the electrode assembly 1formed of mono-cells. That is, the electrode assembly 1 of theembodiment of the present disclosure may have an improved degree ofstructural freedom.

In the present disclosure, a stepped unit cell including a first areaelectrode having a comparatively large area and a second area electrodehaving a comparatively small area may be disposed on a first electrodestack in such a manner that the first or second area electrode faces thefirst electrode stack, and the first or second area electrode may havethe same area as the area of an electrode of the first electrode stackfacing the first or second area electrode. Alternatively, the first areaelectrode may be disposed to face an electrode stack constituted byelectrodes having an area larger than the area of the first areaelectrode so as to form a stepped portion, and the second area electrodemay be disposed to face an electrode stack constituted by electrodeshaving an area smaller than the area of the second area electrode so asto form a stepped portion.

For example, a first stepped bi-cell may include positive and negativeelectrodes having a comparatively large area and a positive electrodehaving a comparatively small area, and the positive and negativeelectrodes having a comparatively large area may be disposed to face afirst electrode stack having the same area as the positive and negativeelectrodes. In this way, two layers having areas decreasing in theheight (vertical) direction thereof may be formed, and a single steppedportion may be formed on the two layers.

Alternatively, the positive electrode of the first stepped bi-cellhaving a comparatively small area may be disposed on a second electrodestack having the same area of the positive electrode or may be disposedon a relatively large electrode of a second stepped bi-cell having thesame area as the positive electrode may face. In this way, two layershaving areas increasing in the height (vertical) direction thereof maybe formed as an electrode assembly having a single stepped portion.

For example, a comparatively large electrode of a stepped unit cell maybe disposed to face a first electrode stack, and the comparatively largeelectrode may have an area smaller or larger than the electrode area ofthe first electrode stack. For example, an electrode of the stepped unitcell having an area smaller than the electrode area of the firstelectrode stack may be a comparatively large electrode of the steppedunit cell and nay face the first electrode stack. Alternatively, anelectrode stack having an area smaller than the area of a comparativelysmall electrode of the stepped unit cell may be disposed on thecomparatively small electrode of the stepped unit cell. In this way,stepped portions may be formed between the first electrode stack and thestepped unit cell. That is, three layers having areas increasing ordecreasing in the height (vertical) direction thereof may be formed asan electrode assembly having two stepped portions.

As described above, a comparatively large electrode of the stepped unitcell located on an interface of the stepped unit cell forming a steppedportion may be a negative electrode. In addition, a comparatively largeelectrode disposed on an interface between the first electrode stack andthe stepped unit cell may be a negative electrode.

The first electrode stack and the stepped unit may be stacked in such amanner that mutually-facing electrodes of the first electrode stack andthe stepped unit may have different polarities. If negative and positiveelectrodes are alternately arranged in an electrode assembly asdescribed above, a battery reaction may occur throughout the electrodeassembly, and thus the capacity of the electrode assembly (battery) maybe increased.

According to an embodiment of the present disclosure, a first steppedunit cell including a first area electrode having a comparatively largearea and a second area electrode having a comparatively small area maybe disposed on a first electrode stack, and a second electrode stackincluding electrodes having the same area may be disposed on the secondarea electrode of the first stepped unit with a separator disposedtherebetween so as to form an electrode assembly. At this time,mutually-facing electrodes of the first stepped unit cell and the secondelectrode stack may have different polarities, and the area of each ofthe electrodes of the second electrode stack may be equal to ordifferent from the area of the second area electrode. If the area ofeach of the electrodes of the second electrode stack is different fromthe area of the second area electrode of the first stepped unit cell, astepped portion is formed at an interface between the first stepped unitcell and the second electrode stack, and the larger of the electrodesmutually facing each other at the interface may be a negative electrode.

Then, the electrode assembly may have a first layer formed by the firstelectrode stack and the first area electrode (having a comparativelylarge area) of the first stepped unit cell (stepped bi-cell), and asecond layer formed by the second area electrode (having a comparativelysmall area) of the first stepped unit cell and the second electrodestack. Alternatively, the electrode assembly may have a first layerformed by the first electrode stack and the first area electrode of thefirst stepped unit cell, a second layer formed by the second areaelectrode of the first stepped unit cell, and a third layer formed bythe electrodes of the second electrode stack smaller than the secondarea electrode.

Alternatively, in the electrode assembly of the embodiment of thepresent disclosure, a second stepped unit cell may be disposed on thesecond area electrode of the first stepped unit cell with a separatordisposed therebetween. In this case, a comparatively large electrode ofthe second stepped unit cell may be a negative electrode, andmutually-facing electrodes of the first stepped unit cell and the secondstepped unit cell may have different polarities. In addition, the areaof an electrode of the second stepped unit cell facing the second areaelectrode of the first stepped unit cell may be equal to or differentfrom the area of the second area electrode. For example, a steppedportion may be formed at an interface between the first stepped unitcell and the second stepped unit cell because the area of the secondarea electrode of the first stepped unit cell is different from the areaof a first area electrode of the second stepped unit cell. In this case,the larger of the electrodes facing each other at the interface betweenthe first and second stepped unit cells may also be a negativeelectrode.

Then, the electrode assembly may have a first layer formed by the firstelectrode stack and the first area electrode of the first stepped unitcell, a second layer formed by the second area electrode of the firststepped unit cell, and the first area electrode of the second steppedunit cell, and a third layer formed by the second area electrode of thesecond stepped unit cell. Alternatively, the electrode assembly may havea first layer formed by the first electrode stack and the first areaelectrode of the first stepped unit cell, a second layer formed by thesecond area electrode of the first stepped unit cell, a third layerformed by the first area electrode of the second stepped unit cell, anda fourth layer formed by the second area electrode of the second steppedunit cell.

An exemplary electrode assembly 1 is schematically shown in FIG. 8according to an embodiment of the present disclosure. Referring to FIG.8, the electrode assembly 1 is formed by disposing a first stepped unitcell 31 on a first electrode stack 41, and disposing a second steppedunit cell 33 on the first stepped unit cell 31. The electrode assembly 1has a width decreasing in the height direction thereof, and two steppedportions are formed on the electrode assembly 1. The first electrodestack 41 includes negative and positive electrodes 5 and 3 that arealternately stacked with separators 7 disposed therebetween.

The first stepped unit cell 31 and the second stepped unit cell 33 arean A-type bi-cell 23 and a C-type bi-cell 21, respectively. In the firstand second stepped unit cells 31 and 33, negative and positiveelectrodes are alternately stacked. In addition, the larger ofmutually-facing electrodes of the first and second stepped unit cells 31and 33 is a negative electrode, and the smaller of the mutually-facingelectrodes is a positive electrode.

The scope and spirit of the present disclosure are not limited to theabove-described electrode assemblies. That is, first electrode stacks,stepped unit cells, second electrode stacks, and second unit cells maybe variously combined to form various electrode assemblies.

In the present disclosure, non-limiting examples of unit cells used toform electrode assemblies include stacked type unit cells, stacked andfolded type unit cells (winding type or Z-folded type), and combinationsthereof. Furthermore, in the present disclosure, electrode assembliesmay be formed by stacking stacked type unit cells or stacked and foldedtype unit cells, or may be formed by stacking stacked type unit cells,and stacked and folded type wilt cells. That is, unit cells of electrodeassemblies are not limited to a particular type.

In the present disclosure, the outermost electrodes of an electrodeassembly may be negative electrodes or positive electrodes, or may be anegative electrode and a positive electrode, respectively. In addition,the outermost electrodes of an electrode assembly may be one-side-coatedelectrodes. The term “one-side-coated electrode” refers to an electrodein which only one side of a collector is coated with en electrode activematerial and the other side is not coated. In this case, sides of theoutermost electrodes coated with an electrode active material may facewith electrodes having a different polarity to contribute to chargingand discharging reactions of a battery, and the other sides (non-coatedportion) of the outermost electrodes not coated with the electrodeactive material may face the outside of the electrode assembly.

Particularly, if a positive electrode is an outermost electrode of anelectrode assembly, the positive electrode may be a one-side-coatedelectrode. Then, precipitation of lithium may be prevented duringbattery reactions, and thus the stability of a battery may be improved.In addition, if a negative electrode is an outermost electrode of anelectrode assembly, the negative electrode may also be a one-side-coatedelectrode. In this case, the consumption of an electrode active materialmay be reduced to save costs, and the thickness of the electrodeassembly may be reduced by the thickness of an electrode active materiallayer, thereby improving the degree of structural freedom of theelectrode assembly in the thickness direction of the electrode assembly.

Lithium ion secondary batteries or lithium ion polymer secondarybatteries may be manufactured using electrode assemblies of theembodiments of the present disclosure. In this case, an electrodeassembly may be disposed in a battery case, and the battery case may bea pouch or prism type battery case.

In addition, a battery pack including at least two battery cells eachincluding an electrode assembly of the present disclosure may bemanufactured, and a device may include one or more of such batterycells. Examples of the device may be a cellular phone, a portablecomputer, a smartphone, a smartpad, a net book, a light electronicvehicle (LEV), an electric vehicle, a hybrid electric vehicle, a plug-inhybrid electric vehicle, and a power storage device.

1. A stepped electrode assembly comprising: a first electrode stackcomprising at least one first unit cell, the first unit cell comprisingat least one positive electrode and at least one negative electrodehaving the same area and being alternately stacked in a verticaldirection with a separator disposed therebetween; and a second unit cellcomprising at least one positive electrode and at least one negativeelectrode that are alternately stacked in the vertical direction with aseparator disposed therebetween, the second unit cell disposed on a sideof the first electrode stack with a separator disposed therebetween,wherein the second unit cell comprises a first area electrode having thesame area as an electrode area of the first electrode stack and a secondarea electrode having an area different from the area of the first areaelectrode, wherein the second unit cell is a stepped unit cellcomprising a stepped portion formed by an area difference between thefirst and second area electrodes.
 2. The electrode assembly of claim 1,wherein the first and second area electrodes of the stepped unit cellface each other, and one of the first and second area electrodes havinga comparatively large area is a negative electrode.
 3. The electrodeassembly of claim 1, wherein the stepped unit cell is an A-type bi-cellcomprising positive electrodes on both sides thereof and a negativeelectrode disposed therebetween, or a C-type bi-cell comprising negativeelectrodes on both sides thereof and a positive electrode disposedtherebetween.
 4. The electrode assembly of claim 3, wherein the steppedunit cell is a stacked type unit cell or a stacked and folded type unitcell.
 5. The electrode assembly of claim 2, wherein a second electrodestack comprising electrodes having the same area as the area of thesecond area electrode of the stepped unit cell is disposed on the secondarea electrode of the stepped unit cell with a separator disposedtherebetween, and the second area electrode and an electrode of thesecond electrode stack facing the second area electrode have differentpolarities.
 6. The electrode assembly of claim 2, wherein a secondelectrode stack comprising electrodes having equal areas different fromthe area of the second area electrode of the stepped unit cell isdisposed on the second area electrode of the stepped unit cell with aseparator disposed therebetween, and the second area electrode and anelectrode of the second electrode stack facing the second area electrodehave different polarities.
 7. The electrode assembly of claim 6, whereina larger of the second area electrode and the electrode of the secondelectrode stack facing the second area electrode is a negativeelectrode.
 8. The electrode assembly of claim 2, wherein a secondstepped unit cell is disposed on the second area electrode of thestepped unit cell with a separator disposed therebetween, and anelectrode of the second stepped unit cell facing the second areaelectrode of the stepped unit cell has the same area as the second areaelectrode but a polarity different from that of the second areaelectrode.
 9. The electrode assembly of claim 8, wherein a comparativelylarge electrode of the second stepped unit cell is a negative electrode.10. The electrode assembly of claim 2, wherein a second stepped unitcell is disposed on the second area electrode of the stepped unit cellwith a separator disposed therebetween, and an electrode of the secondstepped unit cell facing the second area electrode of the stepped unitcell has an area and polarity different from those of the second areaelectrode.
 11. The electrode assembly of claim 10, wherein a larger ofthe second area electrode and the electrode of the second unit cellfacing the second area electrode is a negative electrode, and acomparatively large electrode of the second stepped unit cell is anegative electrode.
 12. The electrode assembly of claim 1, wherein theelectrode assembly is a stacked type electrode assembly or a stacked andfolded type electrode assembly.
 13. The electrode assembly of claim 1,wherein each of outermost electrodes disposed on both sides of theelectrode assembly is independently a negative electrode or a positiveelectrode.
 14. The electrode assembly of claim 13, wherein at least oneof the outermost electrodes is a one-side-coated electrode.
 15. Asecondary battery comprising the electrode assembly of claim
 1. 16. Thesecondary battery of claim 15, wherein the electrode assembly isdisposed in a battery case.
 17. The secondary battery of claim 16,wherein the battery case is a pouch type case.
 18. The secondary batteryof claim 15, wherein the secondary battery is a lithium ion secondarybattery or a lithium ion polymer secondary battery.
 19. A battery packcomprising at least two secondary batteries as claimed in claim
 15. 20.A device comprising at least one secondary battery of claim
 15. 21.(canceled)